Going back to the old job - first and foremost, they don't know how much you're making at your new job. I'm sure they assume its at least 10k more per year than they were paying you. So when they ask if you'd be interested in coming back, you have to give them a number that'll make them choke on their clams.

Seriously, tell them you're quite happy where you are, but for $20k (or 20%) more than what you left at, you'll make the move.

If they want you back, it'll cost them. You got them where you want them, and now turn it in to cash.

I left my job for 9 months. They practically begged me to come back, and I whopped them with my demands, and they agreed.

in all seriousness...NEVER EVER EVER EVER EVER EVER EVER EVER go back to an old job.

This!

Not unless they offer you a seven figure signing bonus, guaranteed money, an iron-clad multi-year contract voidable only by you, get to choose your boss, dictate the hours worked, insane stock options, performance (or lack of) bonuses, and last but not least, the most awesome benny, Mezz PSL's (investment gold, I am told).

in all seriousness...NEVER EVER EVER EVER EVER EVER EVER EVER go back to an old job.

This would be the third time they hired me since 1998. Actually the fourth, but one time I was just a temporary consultant. I crush them with new demands every time. During those stints I've turned down two significant promotions that would have resulted in me spending too much of my day interfacing with bean-counting suits as opposed to the creative folks who make coming to work awesome. This is my roundabout way of significantly ratcheting up the paycheck, perks and bennies without being saddled with certain of the soul-crushing, mind-numbing responsibilities.

It may not be everyone's idea of a career path, but it's working like a charm for me.